The 'Big Dipper': The nature of the extreme variability of the AGN SDSS J2232-0806

Daniel Kynoch, Martin J. Ward, Andy Lawrence, Alastair G. Bruce, Hermine Landt, Chelsea L. MacLeod

Research output: Contribution to journalArticlepeer-review


SDSS J2232-0806 (the 'Big Dipper') has been identified as a 'slow-blue nuclear hypervariable': a galaxy with no previously known active nucleus, blue colours and large-amplitude brightness evolution occurring on a timescale of years. Subsequent observations have shown that this source does indeed contain an active galactic nucleus (AGN). Our optical photometric and spectroscopic monitoring campaign has recorded one major dimming event (and subsequent rise) over a period of around four years; there is also evidence of previous events consistent with this in archival data recorded over the last twenty years. Here we report an analysis of the eleven optical spectra obtained to date and we assemble a multiwavelength data set including infrared, ultraviolet and X-ray observations. We find that an intrinsic change in the luminosity is the most favoured explanation of the observations, based on a comparison of continuum and line variability and the apparent lagged response of the hot dust. This source, along with several other recently-discovered 'changing-look' objects, demonstrate that AGN can exhibit large-amplitude luminosity changes on timescales much shorter than those predicted by standard thin accretion disc models.
Original languageEnglish
Pages (from-to)2573-2588
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date20 Feb 2019
Publication statusPublished - 1 May 2019


  • astro-ph.GA


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